1. Field of the Invention
This invention relates to photographic cameras in general, and more particularly to a method of establishing accurate and reliable engagement between a front attachment such as a lens assembly and a basic structure which constitutes the camera system.
2. Description of the Prior Art
The invention relates to camera systems which include an attachment such as an interchangeable lens, intermediate tubular member, filter or adapter lens which is required to engage a basic structure such as a camera housing, or lens holder with a very high degree of accuracy with regard to positioning control. This requirement arises due to the fact that any error in co-ordination between the parts, however small, will result in serious failure with regard to assuring adequate lens performance in the particular camera system. A wide variety of coupling methods for such camera systems have been proposed. In the case of interchangeable lenses of standard fixed focal length or of the zoom type as the attachment for the camera housing, the conventional types of coupling devices may be classified into three main categories: one is what is called "multi-revolution screw mounting", as for example, disclosed in U.S. Pat. No. 3,682,069. This device is constructed with an inner and outer screw-thread, the latter being formed on an adapter shell which constitutes the rear end of the lens holder. By bringing this thread into axial alignment with the other and then rotating the lens along with the holder itself relative to the camera housing, a particular position of the holder for angular alignment is first sought. Further rotation is initiated to continue coupling operation as the lead angle of the mating threads is acted upon, until the radial shoulder of the adapter shell comes to abut against the position adjusting surface of the front panel of the camera housing. For assurance of a sufficiently rigid connection between the lens holder and the camera housing, it is required to apply an excess force to the lens holder for frictional rotation between the radial shoulder and the mount reference surface. Such coupling operation as is associated with the establishment of phase coincidence between the two threads followed by a number of revolutions of the lens holder in a fitted manner to the camera housing is troublesome and time-consuming. Another disadvantage is that the final angular position of the lens holder relative to the camera housing depends upon the force exerted to effect the rugged screw connection therebetween. This strong frictional movement of the radial shoulder of the adapter shell over the mount reference surface gives rise to a problem because of unevenness created in that surface and further axial shift thereof due to the wear or scratching of material from the reference surface.
Another category is what is called "bayonet coupling". This device comprises male and female bayonet members fixedly carried on the lens holder and the camera housing respectively. During coupling operation, the male bayonet member is slidably fitted to the female bayonet member and then turned by rotating the lens holder about the optical axis while the camera housing is maintained stationary. In this case, the range of rotation of the lens holder is limited by a stopper provided either in the lens holder or in the camera housing in order to insure that the angular alignment of the lens holder relative to the camera housing in the finally coupled position can be controlled with very high accuracy. This feature makes it possible to provide transmission of mechanical or electrical control signals between the lens aperture mechanism and the diaphragm control mechanism, the latter being incorporated in the camera housing. Likewise as in the aforementioned screw-mounting method, it is impossible to avert the defect that the position defining surface of the camera housing is worn away before a long period of use with frequent interchanges of attachments.
In order to obviate this defect, a third coupling device has been proposed as disclosed in U.S. Pat. No. 3,906,534. According to this proposal, one of the two bayonet coupling members is made movable with reference to its carrier and is constructed in the form of a narrow ring arranged to be journalled around the adapter shell which solidly or rigidly formed as part of the lens barrel or lens holder body. To achieve proper attachment of the lens assembly, after the adapter shell is slidably fitted to the camera housing in an adjusted angular position, the operator must to change the position of his hand from the front part of the lens assembly to the clamping ring constituting the bayonet member in order to turn the ring in the tightening direction. As the adapter shell remains stationary in the accurately adjusted position relative to the camera housing, and since the adapter shell and the lens barrel are essentially formed as a single rigid portion of the lens assembly, the provision of signal transmission, for example for controlling the diaphragm aperture or the shutter speed, may be made there between, and the common disadvantage of the first and second coupling devices, that is, the occurrence of undesired deviation of the positioning between the control elements of the lens assembly and of the camera housing, can be eliminated. But, an alternate disadvantage is introduced because of the requirement of locating the clamping ring in a narrow space adjacent the front panel of the camera housing. Thereby the ease of establishing proper engagement between the lens holder and the camera housing is reduced to a considerable extent because it becomes necessary to grasp a relatively narrow coupling ring located adjacent the camera housing when coupling and decoupling is to be effected. In this third coupling device, the coupling or clamping ring is operated members or rings must be produced at a location so as usually located on the lens holder. When the camera housing is designed to have a forwardly projecting section protruding over the coupling ring, for example, a range finder housing extending from the front panel over the clamping ring, and/or a motor drive unit attached to the bottom of the camera housing, these protuberances make it difficult or impossible for the operator's hand to obtain access to the clamping ring.
Such construction of the coupling device for the attachment of the lens assembly has heretofore diminished the degree of design flexibility which would otherwise allow camera systems or broadened capabilities.
In the lens holder, there are provided a diaphragm mechanism and focusing mechanism for which respective manually operated members or rings must be provided at a location so as to afford ease of operation. As that part of the peripheral surface area of the lens holder which remains stationary during focusing and/or zooming is relatively narrow in the longitudinal direction, such a requirement limits the availability of the space which is intended to be occupied by the clamping ring. Particularly with the camera of reduced size, that space is correspondingly reduced in the longitudinal direction. In addition, the location of the clamping ring is limited to the vicinity of the camera housing. These conventional design features make it difficult to accomplish reliable engagement between the lens assembly and the camera housing.
Since the lens and the camera body though very heavy are connected through the narrow ring whose ends are not fixed permanently to their casing, there is a high possibility that staggering movement of the lens about the optical axis of the camera body will occur. As a result mechanical and optical performance will suffer from the slight external shock. In order to avoid this drawback, the production run of the coupling elements must be performed while holding all of the design parameters to more specific values. This limits the selection of materials from which the elements are made up. Therefore, it is impossible to manufacture the coupling device economically.
With the foregoing in mind, the present invention has for its general object to provide a novel coupling device for camera systems wich will overcome the aforementioned drawbacks of conventional coupling devices.
An object of the invention is to provide a coupling device adapted to be used in attachments which constitute part of the camera system.
Another object is to provide an attachment with a coupling device rendering it possible to establish engagement with a basic structure in an accurately adjusted relative position without the necessity of unduly large modification of the mounting in the basic structure.
Another object is to provide an attachment comprised of an adapter which remains stationary during coupling operation so that reliable transmission of mechanical, electrical or other physical control signals can be assured between the coupled attachment and basic structure.
Another object is to provide an attachment having a coupling device fixedly secured thereto so that the coupling operation can be performed by the operation by grasping the casing of the attachment at desired parts remote from the casing of the basic structure, while nevertheless assuring accurate and reliable transmission of the control signals in the finally engaged position.